The environmental protection and the quality of the leisure time are much respected in the modern world. Therefore, the bicycle becomes a popular vehicle or sports instrument again. A trip meter for providing a plurality of trip data, i.e. the speed and the traveling distance of the bicycle, is mounted on the bicycle widely. Please refer to FIG. 1 which is a diagram showing the assembly of the trip meter secured to the bicycle. A magnetic bar 11 is positioned on one of these spokes 12 and a signal transmitter 13 is secured to the forks 14 of the bicycle. A reed switch is positioned in the signal transmitter 13. Each time the bicycle travels over a specific distance, the reed switch will generate a pulse signal due to the magnetic force of the magnetic bar 11 after the magnetic bar 11 passes through the signal transmitter 13. The pulse signal can be wirelessly received by the trip meter 15 mounted on the handle of the bicycle. According to the frequency of the pulse signals and the diameter of the wheel, a plurality of trip data can be calculated, such as the speed, the time, and the traveling distance of the bicycle.
Please refer to FIG. 2 which is a diagram showing the structure of the trip meter. The trip meter includes a bracket 21 mounted on the handle of the bicycle and a main body 22 secured to the bracket 21. In order to use the trip meter more easily, the main body 22 is detachably secured to the bracket 21.
Please refer to FIG. 3(a) which is a block diagram showing the detail structure of the trip meter 15. The trip meter 15 includes a signal receiving circuit 151, a signal processing circuit 152, a liquid-crystal display (LCD) 153, and a battery 154. The battery 154 supplies the power to the signal receiving circuit 151 through the signal processing circuit 152. After supplying the power, the signal receiving circuit 151 can receive the pulse signal outputted from the signal transmitter and the signal processing circuit 152 electrically connected to the signal receiving circuit 151 can count a number and a frequency of the pulse signal and correspondingly generate an output signal indicative of a plurality of trip data. The LCD display 153 can display these trip data such as the speed, the time, and the traveling distance of the bicycle.
According to FIG. 3(a), these elements are positioned in the main body 22 of the trip meter. When the user stops riding the bicycle, the main body 22 can be detached from the bracket 21. The user can record the trip data shown on the main body 22 and store the main body 22 of the trip meter. In order to store all trip data, all elements must keep in action even though the main body 22 is disconnected from the bracket 21. When the main body 22 is positioned near an electronic device which outputs a wireless electromagnetic signal, the signal receiving circuit 151 may be interfered by this signal and the pulse signal may not be received by the signal processing circuit 152, thereby causing an error in calculating the trip data.
In order to avoid the error caused by other wireless signal, a timing function of the signal processing circuit 152 is added. When the signal processing circuit 152 does not receive any pulse signal, the timer starts. When the time interval is longer than a predetermined time interval, i.e. 10 minutes or 1 hour, the signal processing circuit 152 stops supplying the power to the signal receiving circuit 151 even though the main body 22 is secured to the bracket 21 of the bicycle. Until the user restarts to ride the bicycle, the signal processing circuit 152 supplies the power to the signal receiving circuit 151 again. No error occurs because the signal receiving circuit 151 can not be operated without power. However, the user may take a break during the trip and stop riding the bicycle. When the rest time of the user is longer than the predetermined time interval, the power supplied to the signal receiving circuit 151 through the signal processing circuit 152 is interrupted. The pulse signal of the signal transmitter can not be received by the signal receiving circuit 151 without power, so the trip date can not be recorded and shown on the display. On the other hand, when the rest time is shorter than the predetermined time interval, the signal receiving circuit 152 is still at work. Any wireless signal may interfere the operation of the signal receiving circuit 151 at this time. The signal processing circuit 152 may take the interfering signal as a normal signal and keep supplying the power to the signal receiving circuit 151 when the user takes a rest. Therefore, the wrong operation of the signal processing circuit 152 is avoidless by timing the time interval while the signal receiving circuit 151 does not receive the pulse signal of the signal transmitter.
In order to solve the above problem, the signal receiving circuit 151 is moved to be positioned in the bracket 21. Referring to FIGS. 3(b) and 3(c), there are two methods for designing the structure of the trip meter. In FIG. 3(b), the signal receiving circuit 151 is positioned in the bracket 21. The bracket 21 further includes a battery 155 for supplying the power to the signal receiving circuit 151 and two contacting points 1563, 1564 respectively connected with the contacting points 1561, 1562 on the main body 22. When the main body 22 is detached from the bracket 21, the signal processing circuit 152 is disconnected from the signal receiving circuit 151 and the signal processing circuit 152 may not be initiated by other wireless signal received by the signal receiving circuit 151. However, water cause a damage of these contacting points of the main body 22 so that the bracket 21 and the contacting point must be made of a water-resistant material. Compared to FIG. 3(a), the trip meter in FIG. 3(b) further includes a battery 155 and 4 contacting points 1561.about.1564. The process of manufacturing the water-resistant contacting point is complicated and the cost of the trip meter will be increased.
In FIG. 3(c), the signal receiving circuit 151 is also positioned in the bracket 21. Two contacting points 1565, 1566 are further added to connect the signal receiving circuit 151 and the signal processing circuit 152. There is no additional battery in the bracket 21 for supplying the power to the signal receiving circuit 151. The power of the signal receiving circuit 151 is also supplied by the battery 154. Although the time and the cost for manufacturing the additional battery can be reduced, the process for manufacturing 6 water-resistant contacting points between the main body 22 and the bracket 21 is still very complicated.
In order to remove all the interfering signals, the applicant attempts to design a filter to be positioned in the signal receiving circuit 151. However, these methods for removing signals are varied along with different signals and there are too many types of electromagnetic signals used in the electronic devices. A filter can just remove several types of noise signals and the signal receiving circuit is still interfered by many noise signals. If a circuit is designed to remove most noise signals, the layout of the circuit will be very complicated, resulting in that the manufacturing process and the cost of the trip meter will be increased. Therefore, it is tried by the applicant to deal with the problem encountered with the prior art.